Do plasma cutters need gas?

The short answer

Why people ask this, and why the answer confuses

The question comes from welding. Anyone who has looked at MIG or TIG has already learned that the process needs a shielding gas, that the shielding gas comes in a cylinder, and that the cylinder is usually leased rather than bought.

Plasma uses gas for a completely different purpose. In MIG and TIG the gas shields a molten pool from the atmosphere. In plasma the gas is the cutting medium itself — it is forced through a constricting nozzle, ionized by the arc, and the resulting jet blows the molten metal out of the cut.

Because the gas is doing mechanical work rather than chemical shielding, ordinary air does the job. That is why there is no bottle in the corner of a shop that plasma cuts, and why the running cost of plasma is consumables and electricity rather than gas refills.

What the air actually has to be

"Shop air" is not a low bar, and this is where most disappointing plasma purchases go wrong. Three properties matter.

Clean. Hypertherm's guidance is explicit that shop air must be cleaned to remove contamination. Compressor oil carried into the plasma stream coats the consumables and shortens their life sharply.

Dry. Moisture is the single most common cause of a bad cut. Water in the stream destabilizes the arc, throws the cut off square and wrecks consumables. A tank drain, a water separator and ideally a desiccant filter are part of the machine, not accessories.

Enough of it, continuously. This is volume rather than pressure, and the two get confused constantly. A compressor that reaches the required PSI but cannot sustain the required CFM will cut for twenty seconds and then degrade. Plasma cutter air requirements is the full treatment of CFM and PSI, and why tank size is not the answer.

Machines with a built-in compressor

A small number of machines carry their own compressor, which removes the external air supply entirely. Lincoln's Tomahawk 30 AIR publishes an internal air compressor that needs no external air supply or filter, with an external air connection as standard anyway.

What that genuinely solves: the hidden second purchase. A budget plasma cutter that needs a compressor costing as much again is not a budget plasma cutter, and that arithmetic is what sinks a lot of first plasma buys.

What it costs: capacity, and duty cycle. An internal compressor is sized for the torch it feeds, which constrains the machine to the lower amperage band, and the compressor has a duty cycle of its own on top of the cutter's.

The built-in compressor roundup goes through the trade properly.

What air costs you in cut quality

Air is the right answer for a home shop, and it is not a free one. Hypertherm notes that "some nitriding and oxidation of the cut surface occurs with air plasma", and that "this can cause porosity in welds".

In practice that means an air-plasma cut edge should be cleaned back to bright metal before you weld it. On mild steel a flap disc does it in seconds. On aluminum it matters more, because the oxide is more tenacious and the porosity is more likely.

For cutting parts to shape — which is what a home shop mostly does — none of this is a problem. It only becomes one when the cut face is also the weld prep.

So what does plasma actually cost to run?

Three things, and gas is not one of them.

Consumables. The electrode and nozzle are wear items and they are the dominant running cost. Name-brand consumables last markedly longer than budget equivalents, which is why the cheapest machine is not always the cheapest to own.

Electricity, for both the cutter and the compressor.

Compressor maintenance — draining the tank, changing separator elements, and eventually the compressor itself.

Against a MIG setup with a leased cylinder charging whether you weld or not, that is a genuinely different cost shape. Whether a plasma cutter is worth it adds the numbers up.